Doughboys (1930)

Elmer, rich society loafer, falls for Mary, but she'll have nothing to do with him until (mistakenly thinking that he's hiring a new chauffeur) he accidentally volunteers for the army. Luckily, Mary's signed up to entertain the troops. Unluckily, Elmer's sergeant likes Mary, too. And worst of all, they're all about to ship out for France.